No. There is no platinum ratio.
No...
Applied to focusing lenses and mirrors, including telescopes, binoculars, and cameras, the focal ratio or 'F-number' is (the focal length of the lens or mirror) divided by (its aperture or diameter)
ratios are maths way of say there are eg: 3 boys for 15 so there would be 18 people in the class
multiply by 2